Since no one can be excluded from consumption of public goods, one can find it tempting to exploit them without taking part in the provision. It is even hard to call it hostility in general, for from evolutionary point of view selfish behaviour is rewarded - at least in a short-term outlook. 
It is very likely that in a modern world most of the people are righteous, but even a tiny fraction of the society abusing public goods can spoil the sense of provision of them. If any dishonest behaviour is feasible, it may be a dominant strategy for any agent and it cannot be expected that everybody has the same conscience which would innerly restrain them from doing so. Relying on the idea of human sincerity then is tricky.
This kind of, let's say, moral problem resembles a bit the famous \textit{prisoner dilemma} which is described in the section \ref{sec:gt}.

